Research on Gas-shielded Welding Wire of Circumferential Weld for X80 Pipeline Steel

According to the characteristics of the microstructure and properties of X80 pipeline steel,the Mn-Ni-Mo-Ti alloy gas-shielded welding wire was successfully designed and developed for site welding.The chemical composition,metallurgical structure,impact toughness,tensile strength and hardness of the weld metal were tested.The yield strength of deposited metal of the welding wire was 600 MPa,tensile strength was 645 MPa,and Charpy impact energy(-30 ℃) was 105 J.The site welding result of X80 pipeline steel showed that the weld was with perfect strength and toughness matching,when the tensile strength of weld was 645 MPa,the average value of Charpy impact energy(-10 ℃) was 145 J.The microstructure and fracture apperance of weld were analyzed by using metallographic microscope and scanning electron microscope(SEM),the analysis results indicated that the microstructure of weld mainly are acicular ferrite,a few proeutectoid ferrite and granular bainite,and the fracture is dimple which presents a typical ductile fracture characteristics.